Nut plate assemblies are discrete fittings fastened onto a component or part to threadably attach the component or part to other components, parts, structures, etc. Often nut plates facilitate assembly of parts to be joined and also disassembly of joined parts, such as may be required, for inspection or replacement of parts, etc. In nut plate assemblies, the threaded nut portion is incorporated into and/or is surrounded by an elongated portion or plate, the entire structure of which acts as the nut element in the fastener assembly. The nut element is positioned, often loosely, into a cradle element dimensioned to receive the nut element. The nut element and the cradle, together, are typically referred to as the “nut plate” or “nut plate assembly”. Typically, nut plates are fastened to a part that is to be later joined to another part, or to a larger structure. Nut plates are physically joined, via rivets, into desired joining positions on a part. In this way, riveted nut plates are in position on a part, often in advance of further assembly of the part having the nut plate to another part.
Such rivet installation further requires that holes must be drilled with precision and often countersunk to allow an installed rivet to be substantially “flush” with a part surface after rivet installation. Such countersinking, if performed incorrectly can increase part waste, and the drilling itself, even if performed correctly, is labor-intensive further resulting in increased overall cost.
To retain the nut plate in position on a part, holes are drilled through a part from a first side of the part. The nut plate is then positioned such that the holes in the nut plate align with the drilled holes. A retention tool, such as a “deco”, is used to temporarily assist in positioning sheets of material together, or to pieces such as stiffeners before the pieces are permanently joined. Clecos are installed in holes predrilled through the workpieces. Usually such holes are intended for permanent fasteners installed later. The deco expands on the far side of the workpieces and then draws and clamps the nut plate to the part temporarily while maintaining the desired alignment. Clecos prevent shifting of the workpieces and maintain the alignment of other “open” fastener holes that do not have clecos inserted in them (e.g. holding the nut plate in position relative to the component and keeping the holes in the component and the cradle element of the nut plate aligned.)
Typically, nut plates are installed into a structure when only one side of the structure will be easily accessible, or “open” for accepting tools (e.g., with respect to ease of securing the component to the structure with a fastening tool or tools), and where components are to be attached to the structure after the structure is in an installed orientation, and where at least one side of the structure is less accessible, or “closed”. Aircraft and other vehicular structures present a particular application for the use of nut plates. Typically, the nut portion in a nut plate assembly is initially oriented in a nut plate cradle, or basket component, and the entire nut plate assembly is positioned on the interior, or “blind side” or “closed side” of a component. Once the nut plate is in position, the nut plate assembly is then securely affixed to the structure via rivets that are driven through the first side of the part, then into and through the nut plate.
In some nut plate assemblies, the nut is allowed to move slightly after installation, or “float”, allowing for the nut to move slightly and accurately align with the bolt (that is to engage the nut). Across a typical aircraft, for example, joined structures may require the installation of thousands of nut plate assemblies, requiring the installation of thousands of rivets to secure the nut plate assemblies. Each nut plate installation therefore requires the procurement and use of special alignment tools (drills, clecos, etc.) followed by riveting operations that also require special tools. Therefore, nut plate installations result in a labor-intensive and time-consuming endeavor performed by skilled technicians that adds significant time and cost to the manufacture of such large structures, as well as adding to the total number of parts that must be maintained in inventory, while also adding steps and complexity to assembly protocols. Further, the presence of multi-part nut plate assemblies, and the rivets required to install such assemblies, adds significant overall weight to a large structure.